Al-Li rolled product for aerospace applications
View Patent ↗The present invention is directed to a substantially unrecrystallized rolled aluminum alloy product, obtained from a plate with a thickness of at least 30 mm, comprising 2.2 to 3.9 wt. % Cu, 0.7 to 2.1 wt. % Li, 0.2 to 0.8 wt. % Mg, 0.2 to 0.5 wt. % Mn, 0.04 to 0.18 wt. % Zr, less than 0.05 wt. % Zn, and optionally 0.1 to 0.5 wt. % Ag, remainder aluminum and unavoidable impurities having a low propensity to crack branching during L-S a fatigue test. A product of the invention has a crack deviation angle Θ of at least 20° under a maximum equivalent stress intensity factor Keff max of 10 MPa √m for a S-L cracked test sample under a mixed mode I and mode II loading wherein the angle Ψ between a plane perpendicular to the initial crack direction and the load direction is 75°.
1. A method for producing a substantially unrecrystallized aluminum alloy plate with a thickness of at least 30 mm and up to 60 mm, said method comprising:
a) casting an ingot comprising 2.2 to 3.9 wt. % Cu, 0.7 to 2.1 wt. % Li, 0.2 to 0.8 wt. % Mg, 0.2 to 0.5 wt. % Mn, 0.04 to 0.18 wt. % Zr, less than 0.05 wt. % Zn, and optionally 0.1 to 0.5 wt. % Ag, remainder aluminum and unavoidable impurities,
b) homogenizing said ingot at 490°-510° C. for a duration from 4-15 hours,
c) hot rolling said ingot with an exit temperature of at least 410° C. to a plate with a final thickness of at least 30 mm,
d) solution heat treating by soaking at 490 to 540° C. for 15 min to 4 h, wherein the total equivalent time of homogenization and solution heat treatment t(eq)
t
(
eq
)
=
∫
exp
(
-
26100
/
T
)
ⅆ
t
exp
(
-
26100
/
T
ref
)
does not exceed 30 h, where T (in Kelvin) is the instantaneous temperature of treatment, which evolves with the time t (in hours), and T ref is a reference temperature set at 773 K,
e) cold water quenching,
f) stretching said plate with a permanent set from 2 to 5%,
g) aging said plate by heating at 130-160° C. for 5 to 60 hours.
2. A method according to claim 1 wherein Li+Cu>4 wt. %.
3. A method according to claim 1 wherein Li+0.7 Cu<4.3.
4. A method according to claim 1 wherein the lithium content is from 0.8 to 1.8 wt. %.
5. A method according to claim 1 wherein the lithium content is from 0.9 to 1.4 wt. %.
6. A method according to claim 1 wherein the copper content is from 2.7 to 3.9 wt. %.
7. A method according to claim 6 wherein the copper content is from 3.2 to 3.9 wt. %.
8. A method according to claim 1 wherein the manganese content is from 0.3 to 0.5 wt. %.
9. A method according to claim 1 wherein said hot rolling exit temperature is at least 430° C.
10. A method according to claim 1 wherein said aging is done by heating at 140-160° C. from 12 to 50 hours.
11. A method for producing a substantially unrecrystallized aluminum alloy plate with a thickness of at least 30 mm and up to 60 mm, said method comprising:
a) casting an ingot comprising 2.2 to 3.9 wt.% Cu, 0.7 to 2.1 wt. % Li, 0.2 to 0.8 wt. % Mg, 0.2 to 0.5 wt. % Mn, 0.04 to 0.18 wt. % Zr, less than 0.05 wt. % Zn, and optionally 0.1 to 0.5 wt. % Ag, remainder aluminum and unavoidable impurities, and wherein Li+Cu>4.3 wt. %,
b) homogenizing said ingot at 505-510° C. for a duration from 4-15 hours,
c) hot rolling said ingot with an exit temperature of at least 410° C. to a plate with a final thickness of at least 30 mm,
d) solution heat treating by soaking at 490 to 540° C. for 15 min to 4 h, wherein the total equivalent time of homogenization and solution heat treatment t(eq)
t
(
eq
)
=
∫
exp
(
-
26100
/
T
)
ⅆ
t
exp
(
-
26100
/
T
ref
)
does not exceed 30 h, where T (in Kelvin) is the instantaneous temperature of treatment, which evolves with the time t (in hours), and T ref is a reference temperature set at 773 K,
e) cold water quenching,
f) stretching said plate with a permanent set from 2 to 5%,
g) aging said plate by heating at 130-160° C. for 5 to 60 hours.
12. The method of claim 1 , wherein the method results in a substantially unrecrystallized aluminum alloy plate having a low propensity to crack branching.
13. The method of claim 12 , wherein the substantially unrecrystallized aluminum alloy plate has a deviation angle Θ value of at least 20° for a K eff max =10 mPa √m for a Sinclair sample under mixed-mode load (Ψ=75° ).
14. The method of claim 13 , wherein the substantially unrecrystallized aluminum alloy plate has a deviation angle Θ value of at least 30° for a K eff max =10 mPa √m for a Sinclair sample under mixed-mode load (Ψ=75° ).
15. The method of claim 11 , wherein the method results in a substantially unrecrystallized aluminum alloy plate having a low propensity to crack branching.
16. The method of claim 15 , wherein the substantially unrecrystallized aluminum alloy plate has a deviation angle Θ value of at least 20° for a K eff max =10 mPa √m for a Sinclair sample under mixed-mode load (Ψ=75° ).
17. The method of claim 15 , wherein the substantially unrecrystallized aluminum alloy plate has a deviation angle Θ value of at least 30° for a K eff max =10 mPa √m for a Sinclair sample under mixed-mode load (Ψ=75° ).